16 x 2 LCD Display for LMR SDR 1.1: Why four pins are not used?

Johnson Francis | April 19, 2026 | Amateur Radio (Ham Radio) | No Comments

A 16 x 2 LCD display (16 characters, 2 lines) typically has 16 pins. But in the LMR SDR 1.1 circuit four pins (pins 7, 8, 9, 10) are not being used. That is because they are the pins NOT meant for use in 4 bit mode. They have been designated as data pins D0, D1, D2 and D3. The pins being used are as follows:

1	VSS	Ground (0V)
2	VDD	Power Supply (+5V)
3	V0/VEE	Contrast Adjustment (via 10k Potentiometer)
4	RS	Register Select (0=Command, 1=Data)
5	R/W	Read/Write (0=Write, 1=Read) – Often GND
6	E	Enable (High-to-Low Pulse to latch data)

11	D4	Data Pin 4 (Used in 4-bit mode)
12	D5	Data Pin 5 (Used in 4-bit mode)
13	D6	Data Pin 6 (Used in 4-bit mode)
14	D7	Data Pin 7 (Used in 4-bit mode)
15	LED+	Backlight Anode (+5V or through resistor)
16	LED-	Backlight Cathode (Ground)